1. Field of the Invention
The present invention relates to a suction apparatus for attracting a workpiece in accordance with an action of a pressure fluid at a negative pressure to make it possible, for example, to transport the workpiece.
2. Description of the Related Art
A suction apparatus concerning the conventional technique (see, for example, Japanese Utility Model Publication No. 39-11426) is shown in FIG. 7. The suction apparatus 1 comprises a pad section 2 formed to have a skirt-shaped configuration, and a connector section 3 connected to the pad section 2. The pad section 2 is arranged with an opening/closing valve 6 which is continuously energized downwardly by the aid of a resilient force of a spring 5 installed in a valve chamber 4 formed in the connector section 3. A projection 7, which protrudes downwardly, is formed on the bottom surface of the opening/closing valve 6.
When an unillustrated workpiece is attracted, the opening/closing valve 6 is in a valve-open state such that the projection 7 abuts against the workpiece, and the opening/closing valve 6 is separated from a seat section 8 in opposition to the resilient force of the spring 5 in accordance with the pressing action of the workpiece. As a result, a negative pressure fluid, which has been supplied from an unillustrated negative pressure supply source to the valve chamber 4, is introduced into an internal space of the pad section 2 through a passage 9 which communicates with the valve chamber 4. Accordingly, the workpiece is attracted in accordance with the action of the negative pressure fluid.
In the conventional technique, a vacuum switch (not shown) is known, which is used to confirm whether or not the workpiece is attracted to the suction pad by utilizing a difference in pressure between a state in which the workpiece is attracted and a state in which the workpiece is not attracted. The vacuum switch is arranged with a semiconductor pressure sensor for detecting the pressure of the negative pressure fluid for attracting the workpiece. The vacuum switch changes from an OFF state into an ON state when the pressure changes from the atmospheric pressure at which the workpiece is not attracted, into a pressure which exceeds a preset pressure, in accordance with the detecting action of the semiconductor pressure sensor. Accordingly, it is possible to confirm that the workpiece is certainly attracted to the suction pad.
However, the following inconvenience arises when it is intended to confirm whether or not the workpiece is attracted according to the ON/OFF state of the vacuum switch by detecting the pressure fluid in the valve chamber 4 by using the semiconductor pressure sensor, wherein the vacuum switch is connected to the valve chamber 4 of the suction apparatus 1 concerning the conventional technique by the aid of an unillustrated tube or the like. That is, when the workpiece is not attracted, then the workpiece does not abut against the projection 7 of the opening/closing valve 6, and the opening/closing valve 6 is in a valve-closed state. Therefore, the negative pressure of the valve chamber 4 may exceed the preset pressure for the vacuum switch, and the vacuum switch may be in the ON state.
In other words, in the case of the suction apparatus 1 concerning the conventional technique, the pressure fluid, which is supplied from the negative pressure supply source, is directly introduced into the valve chamber 4, giving a state in which the negative pressure in the valve chamber 4 exceeds the preset pressure for the vacuum switch regardless of the valve-open state or the valve-closed state of the opening/closing valve 6. For this reason, the vacuum switch is always in the ON state irrelevant to the presence or absence of the attraction of the workpiece. Therefore, an inconvenience arises in that it is impossible to confirm whether or not the workpiece is certainly attracted, even when the suction apparatus 1 concerning the conventional technique is provided with the vacuum switch.